1. Field of the Invention
The present invention pertains to methods and apparatus for displaying and/or recording data signals. More particularly, the present invention is related to techniques for high speed information recording, such as by way of modulated laser light. Such recorders, or plotters, find particular application in the field of seismic data analysis and presentation. Seismic information is often acquired in the form of large volumes of time sequential traces requiring sophisticated processing and presentation before analysis is practical.
2. Description of Prior Art
Photographic reproduction plotters are known for use in displaying both high contrast images as well as continuous tone gray scale or variable intensity images, particularly where the plotting system is required to generate image data derived from input data or signals at a very high rate. In the area of digital plotters, it is customary to generate images in dot raster form whereby a dot is represented by a logical one (1), a no-dot is represented by logical zero (0), and the images are comprised of large arrays of ones and zeroes. Images resolution is determined by the number of dots per unit area. As the image resolution is increased, the amount of time required to process the data by computer, as well as the amount of computer memory required to hold the image information increases exponentially.
In such prior art photographic plotters, pure dot raster scans are utilized wherein the recording light beam is caused to sweep across the recording medium in a single line. During such a scan, the intensity of the light beam is varied to print information points by exposing the recording medium to appropriate light intensity levels. When such a scan is completed, the plotter is repositioned to carry out the next adjacent scan. Each scan is effectively one dot wide. However, by combining a great number of such scans, a photographic record of information in the form of an exposed area of recording medium is constructed. Such plotters require that the data to be recorded be broken down and processed according to the individual scan lines that can be effected by the plotter. Thus, for example, where the information to be recorded is in the form of a curve, or trace, that requires a two-dimensional presentation, a great number of successive scans may be required to plot the information. The information for each individual scan must be provided to the plotter independently of the information provided for the other scans. Furthermore, where additional data is provided for plotting in the form of traces, or data curves, which may overlap the original curve plotted, all such overlaping traces must be processed and broken down into individual scan information signals before any of the traces may be plotted. Thus, a large data storage and processing facility may be required for the operation of such a prior art plotter.
The use of lasers in high speed plotters for recording information on light-sensitive media is known. U.S. Pat. No. 3,958,250 discloses an example of such a photographic plotting system. There, a modulated laser beam is caused to repeatedly scan a photographic film while a deflector is periodically advanced to move the position of the laser scan along the film. Another example of a laser beam plotter is shown in U.S. Pat. No. 4,028,732.
In view of the large volumes of data often required to be processed and recorded, a plotter capable of handling such data must be able to record the processed information at a rapid rate. The processing of the data should be carried on independently of the operation of the recording mechanism to the extent that neither activity interferes, or delays, the completion of the other. Furthermore, the plotter should feature high resolution to allow the recordation of a large amount of information without unduly increasing the size, and expense, of the recorder mechanism as well as the data processing facility.